Ampere's Law for a Straight Wire

This magnetic field calculator applies B = μ₀I/(2πr) around a long straight conductor. The field forms concentric circles, with the direction given by the right-hand rule — thumb along current, fingers curling in the field direction.

Reading the Numbers

Results are reported in microteslas, the natural scale for everyday fields. A 10 A wire at 5 cm gives roughly 40 µT — near Earth's own field — and doubling the distance halves the field because of the 1/r dependence.

Multiple Conductors

Entering n parallel conductors carrying the same current scales the field by n, modeling busbars and bundled wiring. Magnetic fields add linearly, so the total is simply n times the single-wire value.